Is this on the front of the trailer, as opposed to the side or the back?
I would worry some about water intrusion when driving in the rain if it's a window on the front of the trailer (and there's no protective cover or something over it). Otherwise, it should be a pretty straightforward if possibly awkward job. RV windows typically are held in place with a clamp ring on the inside with a plethora of screws, and the outside sealed with butyl tape or some very similar caulking material under the flange.